1. Field of the Invention
The present disclosure generally relates to methods and systems for controlling SMA actuators, and more particularly, to methods of and systems for providing overheating protection to an SMA actuator.
2. Discussion of Prior Art
Shape memory alloy (SMA) actuators are activated by heating the SMA material to a temperature that is above a prescribed value. This causes the material to undergo phase transformation from a Martensitic to an Austenitic state, wherein it contracts and in the process is used to do work. Typically, SMA wires are heated through resistive heating by applying an electrical current through the wire. A concern with this approach is overheating (i.e., applying an excess of heat energy above what is required to actuate the wire). Overheating causes longer cooling times, and therefore reduced system response bandwidth, and in some cases may damage the wire. It is therefore desirable to have an effective and robust means of preventing wire overheating. Traditionally, various external sensors and/or mechanical devices such as temperature sensors have been used to alleviate concerns relating to overheating. However, these provisions add to the complexity, costs, and packaging requirements of conventional actuators.